1. Field of the Invention
The invention relates to a planning device generating control data for a treatment apparatus for refraction-correcting ophthalmic surgery, said apparatus using a laser device to separate a corneal volume, which is to be removed for correction, from the surrounding cornea by at least one cut surface in the cornea. The invention further relates to a treatment apparatus for refraction-correcting ophthalmic surgery, said apparatus comprising a planning device of the aforementioned type.
The invention further relates to a method of generating control data for a treatment apparatus for refraction-correcting ophthalmic surgery, which apparatus uses a laser device to separate a corneal volume, which is to be removed for correction, from the surrounding cornea by at least one cut surface in the cornea.
Finally, the invention also relates to a method for refraction-correcting ophthalmic surgery, wherein a corneal volume, which is to be removed for correction, is separated from the surrounding cornea by at least one cut surface formed in the cornea by a treatment apparatus comprising a laser device.
2. Background
In the prior art, the most diverse treatment methods aiming to correct refraction of the human eye are known. The aim of said surgical methods is to selectively modify the cornea so as to influence the refraction of light. Various surgical methods are employed for this purpose. The most common method is presently the so-called laser in situ keratomileusis, also abbreviated as LASIK, wherein a corneal lamella is first detached on one side and folded aside. The detachment of said lamella can also be effected using a mechanical microkeratome or a so-called laser keratome as distributed, for example, by Intralase Corp., Irvine, USA. Once the lamella has been detached and folded aside, the LASIK operation provides for the use of an excimer laser which ablates the corneal tissue thus exposed under the lamella. After a volume located beneath the corneal surface has been evaporated in this manner, the corneal lamella is folded back in its original place.
The application of a laser keratome for exposing the lamella is advantageous as compared to a mechanical knife, because it reduces the risk of infection while improving the cut quality. In particular, the lamella may be produced with a much more constant thickness if laser radiation is used. Also, the cut is generally smoother, which reduces the risk of subsequent optical impediments by this boundary surface which still remains after surgery. However, this method has the disadvantage of requiring the use of two different treatment apparatuses, namely the laser keratome for exposing the lamella, on the one hand, and the laser evaporating the corneal tissue, on the other hand.
These disadvantages are overcome by a method recently implemented by Carl Zeiss Meditec AG and abbreviated by the term FLEX. In this method, a femtosecond laser is used to form such a cut geometry in the cornea that a corneal volume (a so-called lenticle) is separated within the cornea. This corneal volume is then removed manually by the surgeon. The advantage of this method is, on the one hand, that the cut quality is further improved by the use of the femtosecond laser. On the other hand, only one treatment apparatus is required because the excimer laser is no longer employed.
When generating cut surfaces in the cornea by laser radiation, the optical radiation effect is usually taken advantage of to generate an optical breakthrough. It is also known to introduce individual pulses, whose energy is below a threshold value for an optical breakthrough, into the tissue or the material in a superimposed manner such that a separation of material or tissue is also achieved thereby. This concept of cut generation in the corneal tissue allows a great variety of cuts.
The result of treatment remaining in these described laser-surgical methods is a cut in the cornea, and although it is no longer visible to the naked eye after a short time, it never heals due to the particular nature of the cornea, because the cornea is “dead” tissue in this respect. Due to the cut, the parts of tissue above the cut are no longer fixedly connected to the parts of tissue below the cut.
However, a need for re-treatments may arise, namely if either the result of the previous operation is not yet satisfactory in terms of the correction of refraction, or if the previous operation was not sufficiently completed for any reason (e.g. due to termination of the operation).
In the case of an insufficient refractive correction, it is known for the excimer laser-based LASIK operation to lift off the corneal lamella again and to remove additional corneal tissue for re-treatment.
However, this approach is impractical for the FLEX method, because it would not allow a re-treatment to be carried out by the same device as for the previous operation, so that it would be mandatory to keep an extra device ready merely for re-treatments.
For terminated laser-based FLEX operations, in fact, no useful or safe solution is known at all.